Could we geoengineer the climate with CO2?

Schemes for artificially cooling the planet can often seem wild and woolly. The latest such geoengineering scheme is no different&colon; it involves frozen carbon dioxide, Antarctica and a whole lot of freezers. While the proposal is not as daft as it sounds, the numbers may not stack up.

Ernest Agee and colleagues of Purdue University in West Lafayette, Indiana, propose installing gigantic freezers in the heart of Antarctica, where temperatures are already tens of degrees below zero. Once the air inside the freezers is cooled to -140 °C, the carbon dioxide within it will freeze out as “CO2 snow”. The solid CO2 could then be stored underground.

Agee’s calculations suggest that it would be possible to remove 1 billion tonnes of CO2 per year this way, using the energy provided by 16 wind farms, each generating 1200 megawatts of electricity. “There’s a lot of wind energy in the Antarctic,” Agee says.

Feasible?

Their calculations are also rather optimistic, says Tim Kruger of the Oxford Geoengineering Programme at the University of Oxford. For instance, they assume that the power plants are 100 per cent efficient, which is impossible.

Furthermore, CO2 makes up only slightly less than 400 parts per million of the atmosphere. This means for every volume of carbon dioxide that gets frozen, Agee would have to cool 2500 volumes of air – so a lot of the energy used would be wasted.

It will also be difficult to store the CO2 once it is frozen. Either it will have to be permanently cooled below its freezing point, which means running the freezers forever, or the CO2 will have to be stored in sealed chambers that can withstand intense pressure once it warms up and expands.